Method for making metal articles



Jan. 3, 1961 E. A. MAcHA ETAL y Y 2,966,740

.METHOD FR MAKING METAL ARTICLES Filed DGO. 50. 1953 f Edward A. Macho 8| Ernord W. Schuff.

ATTORNEY United States Patent-.Q

'METHOD FOR'MAKING METAL ARTICLES Edward A. Macha, Wilmerding,v and Bernard W. Schuif,

Pittsburgh. Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Penrivsylvana Filed Dec. 30, 1953, Ser. No.`401,236

4 Claims. (Ci. 29--534) Our invention relates to a new and improved method `fortproducing metal shapes and, more particularly, to sizing tubes to small tolerances with reference to the various dimensions of thin-walled tubing.

Heretofore, various methods of producing metal tubing have been employed, but none are capable of producing thin-walled tubing toclose tolerances1 except by machining tubing blanks by various shop practices. can readily be appreciated, accurate machfnina requires accurate machine tools and skilled labor, which results in a product which is expensive to produce to such an extent that any production volume is impractical. The cost` of such'machined tubes has also been greatly increased due to the element of human error and machine faults which inherently attend such precision Work. Aside from the cost disadvantage of machine tubes, they are also undesirable due to the physical characteristics of machined metal. Thus, the stresses induced by .ma-

ohining cannot be relieved by annealing when trying Vto l produce a close tolerance product as such annealing:

would destroy the tolerances of the` tube. For thev same reason, hard spots or inclusfons within theA tube 'itself cannot be relieved by any annealing method.

Accordingly, one object of our invention is to provide a new and improved method for forming metalV shapes. Another object of our invention is to provide a new and improved method of producing metal shapes to accurate dimensions.

Still another object of our invention -is to provide a new and improved method for sizing tubes toA accurate dimeri-Y sions.

Another. object of our invention is to provide a new and improved method for producing thinwalled tubes one of which hydraulic connections are made, and anV illustrative method of applying shock to the sizing cylinder- Broadly speaking, our invention entailsk placing a hollow member which is to be formed, and which has its ends plugged, within a stationary member and 'thereafter expanding the hollow member byV hydraulic pressure so that it is in intimate engagement'wth the stationary member. As a consequence of expanding the hollow member, stresses are induced in the member which are relieved by applying'forces to the stationary member While Athe hollow member is subject to the hydraulic pres- Slll'e.

As fwillbe noted, in practicing our invention, a stationLl' ary 'member is utilized into which a movabler member" is Asl ICC

positioned.v For the purposeofvabettcr'understandin of our invention, it is believed that a description with; reference to a relatively long cylindrical tube in the order" of 50 to 60 inches in length will best illustrate our meth- Y It will be realized, however, that the" principles of, our invention are equally applicable to producing shorter; lengths and other shapes, and that in such productionthe" apparatus required may vary onlyas to size.

Referring to the drawing, it will be noted that ,the

tionary member comprises an elongated upright sizi cylinder v2 having an extendingange4 at its lower edge'y which may be secured by any suitable means, such as byfJ bolts 6, to a fixedl member, such as a bed plate v8L C ylfv inder 2 may be formed from any suitablematerial, such," as steel, whichis capable of withstanding relatively high.- pressures and which maybe provided on its interior ksui'-` aces with arsinooth accurately sized bore 10.y Flangel 4 may also be fabricated from steel 'so that it may readily be secured to sizing cvlinder 2 by any suitable means, such as a continuous fillet weld 12.

yThe movable member comprises a sub-assemblywhich'v is assembled separately and inserted within'cylinder 2 as" a unit. The moveblemember comprises a tie rod 14Vr having threaded extending ends 16 of a smaller diameter i thanthe diameter of the tie rod414 so that a shoulder 18 Y is 'formed ateach'end of tie rod 14.y As can be appreciated, in producing long length tubes,'a tie rod 14 of suchf a lengthis comparatively heavy and may not easily be handled by hand, therefore, in assemblingthe movable'-l members, the tie rod 14 may be elevated by means ofma crane hook engaging the eye of an eye bolt (not shown) which may be engaged in a threaded centrally locatedf' hole (not shown) in the upper end 16 of tie rod '14,"

While tie rod 14 is inthe elevated position, a disc 20 having a threaded central opening 22 may be threadedly;v secured to the lower threaded end 16 of the tieV rod 14 until disc 20 engages shoulder 18.` Disc 20 and tie `rod i 14 may be then placed on a suitable elevated platform,

preferably smaller in diameter than disc 20, so that-av tube 24, which is to be sized, may be placed over the discl 20 and tie rod 14, and so that the upper threaded end 16 of tie rod 14 extends beyond the upper end of tube24f,

Thereafter, an upper disc 26 having a threade'ldcentral opening 28 is threadedly secured to the upper threaded end 16 of rod 14, and rests against the upper shoulder',l

1t? of the tie rod 14. The upper disc 26 is also providedl with a pair of threaded openings 30 into which eye bolts may be secured so that the entire sub-assembly may be i elevated by the eye bolts from the support. After the support has been removed,` tube 24 is placed upon theY bed plate 8, and the tie rod 14, with discs 20 and 26at-f tached, is lowered so that the lower disc 20 is flush withV the lower edge of the tube 24. It will'be noted that each-- disc 20 and 26 is provided with a peripheral groove'- having an O-ring gasket, which may be of any suitable I resilient material, such as a synthetic elastomer, to seal the openings 34 between the sides of discs 20 and 26 andl 'l tube 24,

Although the variations of the inside diameter of tube 24 are unsatisfactory from a product standpoint, theyf are not of such a magnitude as to prevent utilizing a.

single size O-nngs 32 to frictionally engage'the, insideV over'the movable member.

At this point, the movable member sub-assembly is com-f plete. with the` tubev Z4 to be formedy mounted' thereor'" and is next lifted and inserted into the"stationary Patented Jan. 3, 1961 3 tube'2. "It should be noted that discs 20 and 26 and tie rod 14 are formed from any suitable material, such as steel, which can withstand the operating pressures of our nethod and which may be formed by machining or the ike.

The movable member sub-assembly with tube 24 mounted thereon is then inserted within the sizing cylinder 2 so that the lower disc 20 rests against bed plate 8. Thereafter, the eye bolts are removed from openings 30 in the upper disc 26, and the annular space 36 between tie rod 14 and tube 24 filled with a liquid such as water, oil, etc. through one of the openings 30, the other being used' for venting. A needle valve 38 is then connected to space 36 by means of a pipe 40 threadedly engaging A one of the threaded openings 30. A similar pipe 42 is threadedly secured to the other threaded opening 3f) in disc 26, and is joined to the high pressure line 44 of a hydraulic pump 46 by a coupling 48. Thus, it will be noted that discs 20 and 26, tube 24 and pump 46 form, when valve 38 is closed, a hydraulically sealed space.

After the annular space 36 has been filled with liquid and needle valve 38 is closed, tube 24 is directly coupled to the pump 46 so that by means of the pump 46 the hydraulic pressure may be increased within the tube 24 and force the tube 24 by radially expanding it into intimate engagement with the bore 10 of sizing cylinder 2. As can be seen, the space between the tube 24 and the sizing cylinder 2 must of necessity be of a sufficient diameter to permit the tube 24 to be readily inserted, and at the same time, cannot be of such a large diameter as to permit the tube 24 to expand radially to such a degree that leakage of the high pressure fluid within the annular space 36 would occur past the O-rings 32 of both the upper and lower discs 20 and 26. It can be appreciated, however, that with the ordinary tubing tolerances available on both the internal and outside diameter of commercially supplied tubing, the bore 10 of sizing cylinder 2' and the diameter of discs 20 and 26 can be predetermined so that no leakage will occur past the O-rings 32 when the tube 24 is subjected to pressure.

yIn order to carry out the purposes of our invention, azhydraulic pressure must be applied to tube 24 which is suicient to enlarge and force tube 24 into intimate engagement with bore l of sizing cylinder 2. After such engagement, sizing cylinder 2 is then subjected to another force in order to relieve the induced stresses inherent in the enlarged tube 24. As shown in the drawing, an air hammer 50 may be utilized in order to apply shock force waves to the outside surface of sizing cylinder 2. In applying such shock waves bymeans of the hammer 50, the hammer head 52 is made of any suitable relatively soft material, such as certain types of brass or bronze, so that the wear of the shock occurs on the hammer head 52 rather than on the external surface of the sizing cylinder 2. In applying the shock waves, the air hammer 50 is moved both vertically and circumferentially upon the outer surface of sizing cylinder 2, in order to achieve the desired stress relief as hereinafter described, although no definite pattern of movement is required of the air hammer 50. It should be noted that the use of air hammer 50 is merely one illustr'ative means of applying repeated shock forces to the enlarged tube 24 and that other methods of applying a force may be equally satisfactory.

After the induced stresses of the enlarged tube 24 have been relieved, the outside diameter of the enlarged tube 24 is, for all practical purposes, equal to the inside diameter of the bore of the sizing cylinder 2. Thereafter, in order to remove the movable member from the sizing cylinder 2, needle valve 38 is opened permitting the pressure within the annular space 36 to be relieved. Once the pressure in the annular space 36 has been relieved, valve 38 and pipe 40 may safely be removed from the opening 30 in the upper disc 26 and the coupling 48 may safely be broken so that pipe 4.2 may be removed from the other opening 30 in the upper disc 26. In

order to lift the combined weight of the movable mem ber with the tube 24, and the liquid confined therein, the upper flange S4 is engaged by suitable lifting means, such as a crane, whereby the entire movable member and tube 24 may be lifted kfrom the bore 10 of sizing cylinder 2. Although various standard clamping means may be utilized in lifting the movable member, in view of the necessity of removing tube 24 from discs 20 and 26, it has been found practical to drill the sides of the upper extending portion 54 of tube 24 so that a lifting bar may be inserted through the drilled holes having lifting rings at each of its ends which are engaged by a crane hook.

Thereafter, the entire sub-assembly of the movable member is held in elevated position, and a plug 56 which is threadedly secured to a threaded hole 5S located in the bottom disc 20 beneath the annular space 36 is removed so that the water within the annular space 36 may be drained. In order to remove the tie rod 14, with discs 20 and 26 attached thereto, from the inside of tube 24, any suitable arrangement may be utilized, such as by use of a bolt (not shown) threadedly inserted in hole 58 in the bottom disc 20 or threadedly inserted in a hole (not shown) in the lower end 16 of tie rod 14 which thereafter is positioned in a T-slot of a bed plate so that the underside of the head of the bolt engages the underside of the T-slot. By such means, the tie rod 14 is secured against vertical movement and the tube 24 may then be pulled upward by means of the lifting bar' heretofore described.

Although only one form of apparatus utilized in produ@ ing and sizing thin walled tubing is heretofore described and shown in the drawing, it is to be realized that such showing is illustrative only and that the apparatus may take other forms Within the scope of our invention. Also, it should be borne in mind that although the discussion heretofore has been with reference to a tube member 24, our method is equally applicable to producing and sizing other standard shapes such as triangles, rectangles, polyhedrons, etc.

In producing thin-walled shapes or in the sizing of such shapes to close tolerances on the outside diameter, it will be realized that the bore 10 of sizing cylinder 2 must of necessity be accurately machined and preferably be honed to a fine smooth finish. It will be realized that in order to insert a tube 24 which is to be formed within the bore 10 of sizing cylinder 2 some radial clearance between the outside diameter of tube 24 and bore 10 is necessary. Although the clearance may vary as long as the hydraulic seal of O-rings 32 is not broken, a clearance of 1/32 of an inch on the diameter has proven to be satisfactory, so that a radial expansion of im of an inch occurs when pressure is applied internally to tube 24. The principle of subjecting a tube to hydraulic pressure to expand is well known for various forming operations, however, in all such operations, the prior art has not developed any method whereby the induced stresses in the tube 24 wall will be relieved or the ductility increased. In our method, by subjecting the tube 24 to a repeated shock force, the induced stresses are relieved, and this is believed to be due to either a recovery or recrystallization or a combination of the two.

When tube 24 is expanded radially through the small distance indicated, by the application of hydraulic pressure, the tube 24 is in effect cold worked to a degree. As is well known, metals that have been strained by cold working are not stable but tend to revert to a strainbalanced state. Thus, with reference to our process, if the cold working of tube 24 occurs entirely within the elastic range of the material of tube 24, upon release of the hydraulic pressure, the tube 24 will return to its original dimensions. If, however, the cold working occurs in the plastic deformation range of the material of tube 24, the outside diameter of tube 24 when pressure 'is released, -will-be greater due to -the permanent set of the it was expanded.

Cold working in the plastic deformation range is, therefore, unsatisfactory with relation to a nished product, as the dimensions during such cold working cannot be controlled with a high degree of accuracy. Such cold working deformation produces structural changes in the metal and at low degrees of deformation, slip lines appear in those grains in which the slip planes are most favorably oriented for yielding under the resolved shear stress. During such deformation, slip lines appear in an increasing number of grains, the grains tend to rotate, the crystal planes to become curve, and the grains become elongated inthe direction of flow. As is well known, such a deformation is accompanied by an increase in the strength properties and a decrease in the ductility properties. In view of these characteristics of deformation, the degree of permanent set which may occur within tube 24 depends primarily upon the physical characteristics and atomic structure of the tube 24 which, due to the variations in commercially available tubing, is unpredictable to any degree of certainty. Thus, application of pressure alone upon tube 24 is entirely unsatisfactory for producing an accurately dimensioned tube. It is a primary purpose of our invention to relieve the induced stresses by subjecting tube 24 to forces so that a localized yielding occurs regardless of whether tube 24 has been cold worked within either the elastic or plastic deformation range, and the material of tube 24 is repositioned in a strain-free state while the dimensions of the enlarged tube 24'remain unl changed.

When the tube 24 is initially placed within the sizing cylinder 2, it is, with the exception of some residual stresses incurred during fabrication, in a relatively strainfree state. Although tube 24 is in a strain-free state, the atoms are in a continuous state of thermal vibration about mean positions that are symmetrically disposed on a crystal structure. `Apart from relatively minor imperfections, the crystal structure is a geometrically perfect arrangement; however, this arrangement is grossly altered by deformation. As has been indicated, the crystallographic planes become curved and twisted and the atoms no longer have precise mean positions on the crystal lattice, but are distorted to positions less symmetrically disposed. Such a pattern of stresses is obviously characterized by points of unusually high energy peaks which are the points of least stability in the cold worked metal where processes relieving the effects of cold deformation presumably will originate. It is also generally believed that such cold deformation increases the atomic distance between the atoms with an increase in the mean free path of the atoms, that is, the atoms have a larger amplitude of vibration. In view of this unstable crystalline structure, if it is desired to retain the physical dimensions of the cold worked material, we have found that a force is required to relieve the induced stresses, which force must be of a sucient magnitude to cause the velocity of the atoms within the crystalline structure to increase in order that they may assume new strain-free positions.

Our method entails the application of a vibratory force upon the outer surface of sizing cylinder 2 which, by means of the impact energy, causes the atoms of tube 24 to increase their velocity, whereby localized yielding occurs in the various areas wherein the atomic structure has been reoriented.

With relation to the force that is applied, there are several processes which are applicable. Primarily, the atomic structure will tend to readjust itself to a stable state; therefore, it is only necessary to increase the Velocity ofthe atoms so that they are capable of reaching a stable state. If desired, it may be considered that the crystalline structure is initially strained and coupled, as indicated, and may be relaxed to an unstrained crystalline lattice-work. As can readily be appreciated, the

force of the hammer blow causes a series of shock waves to occur in cylinder 2 which yare'transmittedto the en#S larged tube 24. The ield of'influencefof'eachblow isf believed to be limited due to the dampingr or restrictingAA nature of the latticework adjacent to the-#latticeworks which have directly received the-transmitted shock waves.l The maximum effect of each blow is directly under thej head 52 of hammer 50 from which apex the transmitted ff shock waves expand radially.

In view'of the fact that* the atoms within tube 24 have Va random Vpath and 'int view of thedamping qualities mentioned above, it is pref'L erable to apply in rapid sequence a series-'of blows of relatively small magnitude as distinguished from a larger* force per blow kapplied at greater spaced intervals.' Byf. so applying such rapid intermittent'blows over-a limited i area, the atoms within tube 24 receive a number of shock impulses which tend to increase their-initiating velocity] to permit them to become realigned.' Althoughl va large* number and type of blows can be utiliz`ed,"it-has been found that a hammer head of approximately one -andone-l half square inches, operating with an air hammer on The study of the process of recovery in metals has not lbeen sufficiently4J extensive to say with any degree of certainty when recovery may be separated from recrystallization and when the two processes overlap. When the two processes voverlap, however. recovery cannot be distinguished from `recrystallization. of these different behaviors. it is evident that therprocessV by which the induced strain is relieved is not important, but that a strain-free crystalline structure is obtained is important. Recovery is generally considered a change' in the `residual stresses which effects primarily the elastic properties of the metal, but having little effect upon the properties involving strength and ductility, this reduc tion in stress may be associated with the straightening of. bentV slip planes and perhaps'with the healing of ymicro-1 scopic cracks adjacent to points'of severe curvature ofslip planes. Recovery is not, however, a complete relief of stress, but only as a partial relief as a metal which has recovered does not lose its capacity to` recrystallize."

The process of recrystallization involves continuous'. formation of nuclei of new crystals and the growth of these nuclei until the system is constituted entirely of the new grain structure. With increasing degrees of deforme' ation, kan increasing number of points'of .highfstressare' present, leading to recrystallization froma great numberil of nuclei, and finally to a great number of grains and, thus, to a-continually -smaller grain size. Itshould'alsovk be noted that the original grain size effects recrystallization, as the amount of .strain hardening which a given amount of compression, elongation, or torsion .intro-` duces into a metal increases as the grain size decreases. Thus, it will .be noted that by this method, the residual stressesv of the enlarged tube 24 can be relieved-'so that the enlarged tube 24 has an outside diameter accurately conforming to the bore 10 of sizing cylinder 2.

As is obvious from the above discussion, .any ductilev material can be accurately formed by the above method, and a large range of internal pressures may be utilized so long as vthe enlarged tube 24 is caused to expand intoy engagement with the bore 10 of sizing cylinder 2. (Inf producing tubes, a pressure of 1000 to 2000 pounds per square inch has been found to be-satisfactory for our purf poses. It can also be realized that it is immaterial hor;I the tubes 24 are initially fabricated as any ofthe cornmon practices are satisfactory. lIt has been` found in using rolled sheet which is welded along its longitudinal seam, that by our method the area adjacent the weld, has been considerably increased in strength so that in effect there are no annealed areas due to the applicationv of welding heat. It has been found, though, that the Whatever may be the underlying cause '7 inert gas welding processes such as helium and argon arc are more satisfactory, as 'a more uniform weld thickness is obtainable.

As has been indicated by our process, the ductility of the sized tube is considerably higher than machined tubes, which permits such tubes to be used under higher operating pressures than'machined tubes. Also, as the tube has been initially cold worked, the eiect of inclusions upon stress concentration and hardness is minimized due to the metal ow during the cold working. Such inclusions are further relieved by the application of the force to the cylinder 2. Further, due to the localized yielding of the metal, the exterior and interior surfaces f the tube are quite smooth as compared to a mechanically worked surface. It should also be noted that the application of the force to relieve the induced stress in the enlarged tube is not a cold working process in the usual sense wherein the strength properties are increased Iand the ductility properties decreased. Nor is it material by what method the force is applied to obtain the localized yielding 'of the metal. i

The importance of our method, apparatus and product can best be understood with reference to the dimensions of a sized tube 24. In this regard by the word dimensions, the measurements or distances in a substantially strainfree state with the internal pressure relieved, is indicated. The best existing commercial tolerances obtainable for welded thin wall cylinders, which are a specialty product having their tolerances substantially reduced with reference to general commercial tolerances are:

Outside diameter +0.0l" on diameters above 3" in Wall thicknesses between 0.012 and 0.024".

Ovality 0.065" for outside diameters above 2" in thicknesses of 0.016" or greater.

Eccentrielty Straight within 0.020" per foot of length.

Thin-walled cylinders produced by our method have tolerances when using 0.021 or 0.025" thick steel within the range of:

Outside diameter +0000, 0.002. Ovality 0.010 to 0.015". Eccentricity Straight within 0.001 per foot of length.

Thus, it will be noted that the percentage of tolerance improvement of cylinders produced by our method over existing specialty products is:

2mm- 002 Outside diameter C Wij-Q32) .065-1315 Ovallty Eccentricity iocl2g2' 0n]=495%.

Having described a preferred embodiment of the invention in accordance with the patent statutes, it is desired that the invention be not limited to the specific construction illustrated, inasmuch as it will be apparent that many modifications in addition to those specifically pointed out herein may be made Without departing from the broad scope and spirit of this invention. Accordingly, it is desired that this invention be interpreted as broadly as possible and that it be limited only as required by the prior art.

We claim as our invention:

Y 1. A method for producing metallic shapes from a Yhol-Y low metallic blank comprising subjecting said metallic,n blank to internal pressure transversely enlarging said y metallic blank to denite outer dimensions uniformly substantially along itsentire length whereby stresses are induced in said enlarged blank, and applying shock force to and transversely of said enlarged blank while subject to said pressure, said forces being suicient to relieve said l stresses.

2. A method for producing metallic shapes from a hollow metallic blank comprising placing said blank in a stationary member having a cavity therein substantially con-l forming to the outer desired dimension of said shape, sub jecting said metallic blank to internal pressure to trans, versely enlarge said blank and to hold said enlarged blank in engagement with said cavity whereby stresses are induced in said enlarged blank, and subiecting said sta-` tionary member to shock force, applied substantially transversely of said cavity, said force being suiiicient to reylieve said stresses.

stresses are induced in said cylinder, and subjecting said l stationary member while in engagement with said tubular blank to an intermittent shock force applied randomly and transversely over substantially the entire outer periphery of said stationary member, said shock force being suflcient to relieve said stresses.

4. A method for producing metallic shapes from a hollow metallic blank comprising placing said blank in a stati-onary member having a cavity therein substantially conforming to the desired outer dimensions of said shape, subjecting said metallic blank to an internal hydraulic pressure to expand said blank and to hold said expanded blank in engagement with said Cavity, whereby stresses are induced in said blank, and repeatedly subjecting said stationary member to an intermittent transverse shock force applied at a plurality of spaced points on the outer peripheryV of said member at positions intermediate the ends thereof, said forces being sutiicient to relieve said induced stresses.

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